Probing the Dark Sector Istvan Laszlo Cosmo ‘08 August 28th, 2008

The Dark Sector ~95 % of the Universe is stuff we don’t know ~74% Dark Energy (DE) Accelerated expansion ~21%Dark Matter (DM) Galactic rotation curves

The Simple Picture Together in simplest form get LCDM Pretty successful, but has issues DE as Cosmological constant: Fine tuning/coincidence problems CDM: Matching Observations to Simulations Cuspiness Problem Missing Satellite Problem CDM: Acbar sees an 1.7 sigma detection of excess of power for l>2000 (Reichardt et al. 2008)

Outline Looking past L Looking past CDM Ways to learn about impact of a DE model Looking past CDM Setting constraints on a dark matter interaction

So what is Dark Energy? Quintessence? Interaction with Higher Dimensions? New exotic material? Modified Gravity?

DE as Modified Gravity Laszlo & Bean, Phys. Rev. D 77 024048 (Jan 30, 2008). Treat DE as a generally parameterized modified gravity theory as in Stabenau and Jain (2006), and Tsujikawa (2007) Goal is to simulate affected observables quickly and reliably matter power spectrum and weak lensing convergence power Compare fast approach of linear simulation with fits to get to nonlinear power to the reliable approach of full nonlinear simulations (Gravity Only PM code of Klypin and Holtzman, 1997)

The Fits Two standard fits They Can modified gravity break the fits? Smith et. al. Peacock & Dodds They Ultimately both rely on the applicability of the Zel’dovich approximation Can use linear growth factor and initial displacement to extrapolate to later time. Fit a transition between purely linear and purely nonlinear scales via simulations of standard gravity Can modified gravity break the fits? Change critical density for collapse Change scale at which nonlinear effects become important

Evolution Equations Working in Newtonian Gauge Poisson’s and Peculiar acceleration equations where describes a change in the relationship of potential to over-density such as and we add some extrinsic shear as

Models Given this parameterization we can incorporate quite a wide range of modified gravity theories F(R,F,C) (as in Tsujikawa 2007) Scalar-Tensor theories Also includes Quintessence, k-essence We therefore choose 4 models to explore the parameters’ effects

DE Models Choose models that involve/are mixtures of Scale dependent modification to Poisson’s Equation Scale independent modification to Poisson’s Equation Scale independent anisotropic shear

A Sample Result

DE Conclusions For a wide range of modified gravity theories we can utilize the and parameterization For things describable by this parameterization, we can use the quick approach to compare theories and observations at least at these scales, ie in the mildly nonlinear regime

Interacting DM Bean, Flanagan, Laszlo, & Trodden, http://arxiv.org/abs/0808.1105

DM Work : Model Consider a Lagrangian for DM of the form A scalar field mediates interaction via Yukawa coupling Interaction length scale set by mass of scalar field particle Relativistic so motion is adiabatic. Thus energy is conserved aside from expansion can show rs=sqrt(energy/numberdens^2/coupling^2) So E down with exp is ~a^-1 number dens is a^-3 so rs ~ sqrt a^2~a is comoving L top Freiman and Gradwohl or nUsser Gubser and Peebles

DM Work: Model This results in a total potential for the DM with From which we see that Thus the growth of perturbations is altered

DM Work: Sample CMB Theta=180/l and L= k\eta, Height difference in peaks indicates baryons. Peak is remnant harmonic of sound waves first peak at 1 degree or so means flat Peaks from inflation since suggests in place early as have harmonics and thin peak Originally all together, neutrino free so flattens out, DM free and no press so sits there grows, Bary and phot move out decouple then bary leaves peak on dm as the two group into sync Though beta >-0.5 implied by Frieman and gradwohl we take >0 <0 shifts peaks up at highl but doesn’t impact tail reverses the effect or rs to some extent

DM Work: Results At 95% confidence <3.9 for 1 Mpc, and <1.05 at 10 Mpc Chisquared best was 1353.987 for the yukawa interaction, 1354.112 for standard case. (and mean log like was 1357.108 vs 1357.142)

Conclusions Cosmological observables can be used effectively as means of probing both components of dark sector And in particular For modified gravity we can confidently apply the standard fits (at least for mildly nonlinear scales) and so have a quick way to test models For DM showed that l>2000 excess in CMB does not favor interacting DM